1. Field of the Invention
The present invention relates to a liquid ejection head for ejecting liquid such as ink.
2. Description of the Related Art
Inkjet recording apparatus for recording images on a recording medium by ejecting ink are generally equipped with a liquid ejection head for ejecting ink. Known mechanisms by which liquid ejection heads eject ink include those employing a contractible pressure chamber and a piezoelectric element for causing the pressure chamber to contract and reduce the volume thereof. With such a mechanism, the piezoelectric element is deformed as a voltage is applied thereto to thereby cause the pressure chamber to contract so that the ink in the pressure chamber is forcibly ejected from an ejection port formed at an end of the pressure chamber. Shear-mode type liquid ejection heads are known as a type of liquid ejection head having such a mechanism. In a shear-mode type liquid ejection head, one or two of the inner wall surfaces of the pressure chamber are formed by a piezoelectric element and the pressure chamber is forced to contract by applying a voltage to the piezoelectric element so as to cause the latter to generate a shear deformation.
Inkjet apparatus for industrial applications are required to use high viscosity liquid. Then, the liquid ejection head of such an inkjet apparatus is required to provide high power for liquid ejection. To meet the requirement, Gould type liquid ejection heads having a pressure chamber formed by a cylindrical piezoelectric member that represents a circular or rectangular cross section have been proposed. In Gould type liquid ejection heads, the piezoelectric member is deformed uniformly in radial directions relative to the center of the pressure chamber to cause the pressure chamber to expand or contract. In Gould type liquid ejection heads, all the wall surfaces of the pressure chamber are deformed and the deformation contributes to the power for ink ejection and hence the Gould type liquid ejection head can provide high power for liquid ejection if compared with the shear-mode type liquid ejection head in which only one or two inner wall surfaces of the pressure chamber are formed by a piezoelectric element.
For a Gould type liquid ejection head to achieve a higher image resolution, a plurality of ejection ports need to be highly densely arranged. Then, as a result, pressure chambers that correspond to respective ejection ports also need to be highly densely arranged. Japanese Patent Application Laid-Open No. 2007-168319 discloses a method of manufacturing a Gould type liquid ejection head in which pressure chambers can be highly densely arranged.
According to the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319, a plurality of grooves extending in the same direction are formed on each of a plurality of piezoelectric plates. Subsequently, the piezoelectric plates are laid on one another such that the grooves are aligned, and then cut in a direction orthogonal to the extending direction of the grooves. The groove portions of the piezoelectric plates that are cut apart form the inner wall surfaces of the pressure chambers of the liquid ejection head. Thereafter, the piezoelectric members interposed between adjacent pressure chambers for separating the pressure chambers are removed to a predetermined depth. As the pressure chambers are completely formed, a supply channel plate and an ink pool plate, and a printed circuit board and a nozzle plate are connected to the tops and the bottoms of the piezoelectric plates to produce a complete liquid ejection head. Thus, with the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319, pressure chambers can be arranged in a matrix and highly densely. Additionally, with this manufacturing method, pressure chambers can be formed highly precisely because an operation of forming grooves on piezoelectric plates can be executed more easily than an operation of forming holes in piezoelectric plates.
A plurality of pressure chambers are separated by spaces in a liquid ejection head manufactured by the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319. Therefore, if the liquid ejection head is made to include pressure chambers having a large length (height) for the purpose of ejecting high viscosity liquid (by boosting the power for ejecting liquid), the rigidity of the liquid ejection head is inevitably reduced. As the rigidity of such a liquid ejection head is reduced, the structure surrounding the pressure chambers is apt to be broken to make the liquid ejection head no longer possible to eject liquid in some instances.
Meanwhile, Japanese Patent Application Laid-Open No. 2007-118611 and Japanese Patent Application Laid-Open No. 2008-087288 disclose methods of driving liquid droplets located in and near the nozzles of a liquid ejection head to circulate during a printing operation in order to prevent dust, dried ink and foreign objects from accumulating in the nozzles and suppressing the lingering of air bubbles in the nozzles. However, these patent documents do not represent any circulation channel structure that is effective for Gould type liquid ejection heads including a plurality of two-dimensionally arranged pressure chambers.